$ A = \left[\begin{array}{rrr}2 & 1 & 2 \\ 2 & 2 & 0 \\ 1 & 0 & 0\end{array}\right]$ What is $ A^{-1}$ ?
Explanation: $ = \left[\begin{array}{rrr}0 & 0 & 1 \\ 0 & \frac{1}{2} & -1 \\ \frac{1}{2} & -\frac{1}{4} & -\frac{1}{2}\end{array}\right]$